There are three parts to a well-built story:
They support each other and prop each other up.
The plot, the story’s shape, can’t exist without knowing the characters’ wants and helps drive the story to its outcome.
In return, your characters help build your plot. Who they are, what they struggle with, and where they are coming from all hint at the obstacles, actions, and responses they will take through their journey.
And a well-integrated theme reflects the character’s journeys. The struggle they face and the pros and cons of getting what they want are all representations of the theme—whether or not you intended for them.
Each piece lifts the other. Understanding this puts you in control of the impact your story makes.